Laminated printed circuit architectures employed for RF (microwave/millimeter wave) applications use a variety of feed-through configurations for transporting RF signals between opposite sides of a substrate laminate. One of these structures, shown diagrammatically in plan in FIG. 1, distributes a plurality of ground vias (four being shown at 11, 12, 13 and 14 in FIG. 1) around an RF feed-through pin 15 which, in turn, is connected to a microstrip launch conductor 16. A problem with this approach is the relatively poor shielding offered by the ‘punctuated’ arrangement of spaced apart ground vias, which typicaly results in leakage to one or more internal layers of printed circuit conductor traces. In addition, the feed-through suffers from transition mismatch, making the RF pass-through lossy and degrades the voltage standing wave ratio (VSWR).
Another structure, termed ‘sloppy coax’ and disclosed in U.S. Pat. No. 6,166,705, is shown in cross-section in FIG. 2. This structure has a plated aperture 20 through the substrate laminate 21, the plated aperture being conductively connected to ground plane conductors 22 and 23 on opposite surfaces of the substrate. RF throughput is provided by an insulated wire 24, which is bonded to an RF terminal pad 25 on one side of the substrate, inserted through the plated aperture 20 and then terminated at an RF pad 26 on the opposite side of the substrate. A dielectric layer 27 surrounds the conductor within the aperture 20. A problem with this structure is the fact that its manufacture is labor-intensive (in passing the RF conductor through the plated aperture and making the wire bonds to the RF terminal pads). In addition, in order to make connections to the RF terminal pads, the wire contains respective loops 28 and 29, which add unwanted inductance and serve as above-the-surface radiators.